Battery life or power efficiency is a major performance criterion for wireless communication devices and many other types of wireless transmitters. Power efficiency has become more important as wireless communication devices move into the provision of multimedia services, which consume much more power than traditional voice services. Improving the efficiency of the transmitter component of wireless communication devices plays an important role in improving the performance of such devices.
In one aspect of the need for improved power efficiency, such new modulation methods as Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiplexing (OFDM) and other types of multi-carrier modulations, and combinations thereof, exhibit high peak to average power ratios (PAPR) in the transmitted power. Additionally, the PAPR changes with time, depending on a transmission data format configuration. Such high and variable PAPR values require the transmitter (including the power amplifier) to provide large dynamic range and good linearity.
In another aspect of the need for improved power efficiency, in many communication standards, such as cdma2000, 1×EV-DO (1× Evolution Data Only), 1×EV-DV (1× Evolution Data and Voice) and Universal Mobile Telecommunications Service (UMTS), the transmitted power is required to be controlled to vary in a large range, e.g., from lower than −50 dBm to higher than 23 dBm for cdma2000 devices. Furthermore, the speed of power, and PAPR, variation is also very fast. For example, in cdma2000, the speed of power variation is up to 800 dB per second and the PAPR may vary every 20 ms. It is challenging to design a transmitter to work well in all such conditions without sacrificing efficiency in power consumption.
In some known methods to improve transmitter efficiency in varying transmit power and/or varying PAPR transmitters, the transmitter circuits provide one or more control ports to control certain parameters within the transmitter circuits in continuous fashion and/or in digital fashion. The parameters in the transmitter circuits can be any physical quantities that can be used to trade for efficiency at a given condition.
The control ports can control parameters including (but not limited to) bias, power supply voltage, switch in or switch out stages and combinations of these. In particular, the bias to each or some of the amplifying devices inside a power amplifier may be controlled. The objective is to control the bias to an amount no more than necessary to limit out of band spurious emissions as stated by a predetermined requirement and maintain waveform quality for each given transmitted power and/or PAPR values in a supported range. The power supply voltages to all or selected stages of power amplifier and/or other circuits in transmitter may be controlled such that voltage is supplied to the circuits (at least in part) by non-resistive voltage regulating means (e.g., s switching power supply) to obtain the benefit of power saving. The objective is to control the voltage no more than necessary to limit out of band spurious emissions as stated by a predetermined requirement and maintain waveform quality for each given transmitted power and/or PAPR value in the supported range. As well, selected stages may be switched in or out according to the transmitted power and/or PAPR values.
Despite the advances represented by these earlier methods, the optimization of transmitter power efficiency continues to attract significant attention.